The present invention relates to an active matrix type display device, and more particularly is suitably applicable to a liquid crystal display device which performs time-division driving of drain lines.
As a display device which is capable of performing a high-definition color display for a mobile phone, a notebook type computer, a display monitor or the like, various types of flat panel type display devices including a liquid crystal display device which uses a liquid crystal panel, an organic electroluminescence display device (organic EL display device) which uses electroluminescence (particularly organic electroluminescence) element, a field emission type display device (FED) which uses field emission element and the like have been already put into practice or have been studied for future practice.
This type of display device includes a substrate provided with pixels which form an image display region. For example, in one example of the liquid crystal display device which is popularly used as display means, on a main surface of a first substrate which is preferably made of glass and is also referred to as a thin film transistor substrate (TFT substrate), a plurality of pixels having thin film transistors are arranged in a matrix array where the pixels are arranged two-dimensionally in the horizontal direction and the vertical direction, the first substrate and a second substrate (also referred to as a counter substrate) having color filters corresponding to respective pixels are laminated to each other, and liquid crystal is sealed in a lamination gap thus forming the liquid crystal display device. Here, the color filters may be formed on the first substrate side. The liquid crystal display device in which a common electrode (also referred to as a counter electrode) is formed on the second substrate side and the pixels are driven in response to electric fields generated between both substrates is referred to as a vertical field type (TN type) display device.
Here, driving circuits are arranged outside the display region of the first substrate. The driving circuits include a gate line scanning circuit (also referred to as a gate driving circuit) which applies a scanning signal (selection signal) to gates of thin film transistors which constitute pixel circuits of the pixels which are arranged on the display region in a matrix array, and a video signal line output circuit (also referred to as a drain driving circuit) which supplies a video signal to drain electrodes of the thin film transistors which are selected by the gate line scanning circuit.
As other type of pixel driving method of the liquid crystal display device, there has been known a lateral electric field (IPS: In-Plane-Switching) method. This method is a method in which both of pixel electrodes and a common electrode are formed on a first substrate side and liquid crystal is driven based on electric fields generated between the pixel electrodes and the common electrode.
Particularly, in the IPS-method liquid crystal display device, to enhance the transmissivity, the common line adopts a transparent wiring layer (a layer made of ITO or the like) having a relatively high resistance as a wiring layer different from the gate lines and storage lines, and the common line is overlapped with the gate lines and the storage lines. Further, the capacitance between the drain line and other fixed potential is not provided intentionally and hence, is relatively small.
As the driving circuit of the liquid crystal display device, the respective drain lines are usually driven altogether. However, there exists the driving circuit in which to reduce the number of output terminals of the drain driver IC, a time-division switch is formed on the first substrate and the drain lines are driven in a time-division manner. In this case, there exists a period in which the drain line assumes a floating state.
As documents which disclose this type of liquid crystal display device, for example, Japanese Unexamined Patent Publication 2002-151699 (patent document 1) and Japanese Unexamined Patent Publication Hei 11(1999)-327518 (patent document 2) can be named. The patent document 1 discloses a liquid crystal display device in which extension portions of capacitance lines have a width greater than a width of signal lines and, at the same time, alight shielding function is provided with respect to a region defined in a gap of each pixel electrode. Here, in the patent document 1, the time-division driving of the drain lines is not performed. Further, patent document 2 discloses a liquid crystal display device which performs the time-division driving using the dot inversion.